High pressure pumps such as hydraulic intensifier pumps are widely used for applications such as waterjet cutting and abrasivejet cutting that require the delivery of a high pressure of water or other fluids including but not limited to liquids, liquid mixtures, gases and gaseous mixtures. As used herein, the term high pressure shall mean pressure in excess of approximately 3500 psi. For the sake of simplicity, this invention will be described in the context of a high pressure water pump, although those skilled in the art will recognize that this invention is not limited to any particular fluid or fluidic mixture. Similarly, it should be recognized that, although this invention is described in terms of its application to high pressure pumps for a waterjet or abrasivejet cutting system, its application is not so limited, and the invention herein is not restricted to high pressure pumps for any particular application or media.
The high pressure pump of a waterjet or abrasivejet cutting system produces high pressure water that is conducted to the jet-forming orifice of a waterjet or abrasivejet cutting head. As is known in the art of waterjet and abrasivejet (hereinafter, collectively, waterjet) cutting systems, a high velocity waterjet is formed by compressing the water to an operating pressure of 3,500 to 150,000 psi (238 10,204 bars), and forcing the high pressure water through a jet-forming orifice having a diameter of between 0.003-0.040 inches (0.08 1.02 mm).
Historically, high pressure pumps used in waterjet systems are either direct-drive or intensifier type. A direct-drive high pressures pump employs high pressure pistons which are mechanically linked to a drive mechanism. The drive mechanism normally comprises a crank mechanism, connecting links and a power source that rotates the crank. The power source employed is electric, gasoline or diesel for most applications. Direct-drive pumps are normally very efficient (e.g., in the 90% range), in terms of the required power input for producing useful power in the form of pressurized cutting fluid. Current direct-drive high pressure pumps, however, have little or no variation of volumetric flow and are therefore restricted in their ability to safely and successfully power a wide range of orifice sizes at optimum cutting pressure.
An intensifier-type high pressure pump includes a cylinder, a hydraulic working piston, a high pressure piston, inlets for a hydraulic working fluid to both advance and retract the working piston, a water inlet for the ingress of water to be pressurized, and a water outlet for the egress of the pressurized water. In operation, a relatively low-pressure hydraulic fluid is applied to the comparatively large working piston. The working piston, in turn, drives the smaller high-pressure piston. The resulting water pressure is the hydraulic pressure multiplied by the ratio of the hydraulic and high-pressure piston areas.
Intensifier-type high pressure pumps are capable of producing variable volumetric flow coupled with constant working pressure. This allows the user to power a large range of orifice sizes at the optimum working pressure. However, the intensifier type system is not efficient in terms of the power input required for useful power produced in the form of useful pressurized cutting fluid. Efficiencies in the range of sixty to seventy five percent are typical.
The fluid to be intensified (e.g., water) is typically delivered to the intensifier pump via an inlet check valve from a low-pressure fluid supply. The fluid supply is generally is able to generate sufficient pressure to overcome the tension of an internal poppet spring within the check valve, opening the check valve when the intensifier piston is in the intake portion of its cycle, thereby allowing the fluid to be drawn into the intensifier pistons cylinder. When the intensifier piston enters the compression portion of its cycle, the pressurized fluid within the cylinder closes the inlet check valve and is thereby prevented from back flowing into the low pressure supply side of the pump. The pressurized fluid is subsequently expelled from the cylinder by opening an outlet check valve with the increased fluid pressure through compression, and flowing the pressurized water out into the system.
In many cutting facilities, a single intensifier pump is used to feed pressurized water to the jet-forming orifices of a plurality of cutting heads. As the cutting heads are selectively activated and deactivated during their respective cutting operations, or as one or more cutting heads are brought on line or taken off line, the fluctuating volumetric demand for water causes pressure variations in the line; i.e., pressure drops in the line as more water is required, and increases as demand lessens. This requirement has led to a world-wide predominance of variable volume intensifier-type high-pressure pump installations for waterjet applications. The variable volume intensifier-type high-pressure pump has more than compensated for lower operating efficiencies through better reliability, compared to the direct drive pumps now in use in the waterjet cutting industry.
Industrial applications require precise fluid delivery, and pressure fluctuations are accordingly undesirable because the rate, ability and quality of the cutting process can be detrimentally affected. Thus a slowly reciprocating intensifier-type high pressure-pump requires the employment of a vessel capable of holding approximately 100 cubic inches of cutting fluid (e.g., water) at the working pressure to smooth fluctuations in the working pressure of the cutting fluid. Such vessels are referred to as accumulators or shock attenuators. These vessels are expensive, with costs for the end user near (US) $10,000 for a 100 cubic inch (i.e., approx. 1.64 liters) unit.
Direct-drive high-pressure pumps are normally constructed with three or more high pressure cylinders operated at relatively high cycle speeds which smooth the working pressure without the need of the expensive accumulator. Thus, it can be much more economical to manufacture the relatively higher efficiency direct-drive high-pressure pump rather than the relatively lower efficiency intensifier-type pump for this reason as well.